Patent Literature 1 discloses a valve device in which a housing is divided into an upper chamber and a lower chamber by a diaphragm having an opening portion, and the lower chamber stores a float. When fuel enters into the housing, the opening portion is closed by the float so as to prevent leakage of the fuel from an exhaust port of the upper chamber to the outside of the tank.
In the valve device, the opening portion is enclosed in the upper chamber by a cylindrical partition wall. In the partition wall, an exhaust port and a notch portion are formed with the opening portion interposed therebetween. When the liquid fuel enters into the upper chamber, the fuel flows down from the notch portion to the lower chamber through the opening portion.